It can be argued that one of the three alleles is ancestral to the other two. For example, the origin of the O allele, and subsequently blood type O, is simply the result of the deletion resulting in a loss of function of glycosyltransferase activity for the A antigen. A mutation resulting in the loss of function in a protein, at best, would be a "nearly neutral" mutation since blood type O does not appear to have any deleterious effects or selective advantage over the other two blood types.
Famous Type Os
Elvis Presley, Prince Charles, Al Capone, and Queen Elizabeth.
Individuals of Type O blood have the thinnest blood, strongest immune systems, strongest stomach acids, and live the longest of all the blood types. Type Os are however, prone to digestive disorders, more susceptible to arthritis, and thyroid disease due to an overactive immune system. Foods such as wheat and dairy also promote inflammation for this blood type that can trigger an imbalance in immunity.
Type O is the oldest blood type in which people hunted for their food to survive focusing a predominant meat diet. Type O’s are encouraged to eat lean red meats and poultry but limited in dairy products, grains (wheat is high on the list to avoid) and legumes. Although this nutrition is high in animal protein, the type O requires intense physical exercise to help burn off the meat.